ESSEX BIRD-MIGRATION.
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summer residents; on the other hand, near the Equator, the
native birds are mainly sedentary, and migration is almost
entirely due to the appearance of birds, which breed in other
areas. Migration, however, in countries such as our own, which
are situated in temperate zones, is a much more complicated
matter. Our islands are so placed that they are much affected
by the hordes of birds which migrate through the northern
hemisphere to and from their breeding quarters. Then a large
number of our native birds migrates in greater or less degree, both
as to distance and to the number of individuals of the species.
Some species use the British Isles for the purpose of breeding
only, others use it merely as a winter abode, and there is a large
group of birds which do not reside at any time but use our islands
as a halt to some more distant destination. The greater
part of the birds which visit Britain fly from south to north,
and in the opposite direction. The migrations in the British
Isles are still further complicated by important movements
between east and west, probably by reason of our temperate
climate. Britain has thus been shown to be a land of great
activity among birds.
From the movements of birds over the world we have narrowed
our consideration to a tiny portion of the globe, namely, the
British Islands, and now we still further condense our survey
so that we may deal with those movements which may have
relation to the county of Essex. In the first place let us consider
the chief sources of information of Essex bird-migration. Very
few contributions of any length have been made directly to the
subject. E. A. Fitch delivered in 1890 as a presidential
address to the Club, a paper entitled "Bird-Migration," but
this did not claim to deal with Essex. Christy made no effort
to organise this aspect of Essex ornithology, although he gave a
list of the light-stations off the Essex coast in his "The Birds
of Essex." It would appear that the only comprehensive effort
to elucidate the problems of migration in the county is the article
in the present writer's "A History of the Birds of Essex." This
contribution, although it was based on all the matter then in
existence, had to be condensed on the grounds of space and time.
For this reason the present opportunity is welcomed, as it
permits of the presentation of a more detailed account of those
avian movements which are related to Essex. The chief works